1. Field of the Invention
The present invention relates in general to a code division multiple access (CDMA) base transceiver station (BTS), and more particularly to a base transceiver station which comprises outdoor, multibeam active antennas with transmission/reception amplifiers.
The present invention further relates to a base transceiver station with active antennas, for varying the strength of a forward or reverse channel signal in every sector to vary a transmission coverage or reception coverage of the antennas.
2. Description of the Prior Art
In a CDMA mobile communication system such as a digital cellular system (DCS) or personal communication service system (PCS), generally, a base transceiver station comprises omnidirectional antennas or sector antennas installed outdoors, and a high-power amplifier and low-noise amplifier installed indoors. The high-power amplifier is connected to an antenna transmitter, and the low-noise amplifier is connected to an antenna receiver. Such a construction of the base transceiver station is shown in FIG. 1, herein.
FIG. 1 schematically shows the construction of a conventional single-sector base transceiver station in a CDMA mobile communication system.
As shown in FIG. 1, the base transceiver station comprises antennas 11, 12 and 13 installed outdoors, and a transmission/reception filters/low-noise amplifier circuit 20, high-power amplifier 30, transceiver shelf 40, global positioning system (GPS) receiver 50, digital shelf 60 and base station control processor 70, installed indoors.
In the conventional single-sector base transceiver station with the above-mentioned construction, on a forward link, an output signal from the transceiver shelf 40 is amplified by the high-power amplifier 30, filtered by a transmission filter in the transmission/reception filters/low-noise amplifier circuit 20 and then transmitted through the outdoor transmission antenna 11.
On a reverse link, signals are received through the outdoor reception antennas 12 and 13, filtered by a reception filter in the indoor transmission/reception filters/low-noise amplifier circuit 20, amplified to a predetermined level by a low-noise amplifier in the circuit 20 and then transferred to the transceiver shelf 40.
The transceiver shelf 40 acts to up-convert an intermediate frequency (IF) signal from the digital shelf 60 into an ultrahigh frequency (UHF) signal and to down-convert a received UHF signal into an IF signal.
The base station control processor 70 functions to control the entire operation of the base transceiver station. In particular, the base station control processor 70 collects alarm signals generated in the base transceiver station and sends them to a base station controller.
In the conventional base transceiver station of the CDMA mobile communication system, as mentioned above, the omnidirectional antennas or sector antennas are installed outdoors, and the high-power amplifier and low-noise amplifier are installed indoors. However, in the above-mentioned base transceiver station, as the indoor equipment and outdoor antenna part become more distant from each other, the high-power amplifier must have relatively high output power due to an increase in cable loss, resulting in economic losses. Further, such a cable loss may degrade a reception performance of the system.
Moreover, the high-power amplifier should be selectively applied depending on a distance between the indoor equipment and outdoor antenna part, resulting in an inconvenience in installing the base transceiver station.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a base transceiver station which comprises outdoor, multibeam active antennas with transmission/reception amplifiers.
It is another object of the present invention to provide a base transceiver station for varying the strength of a forward or reverse channel signal in every sector to vary a transmission coverage or reception coverage of the antennas.
In accordance with the present invention, the above and other objects can be accomplished by a provision of a base transceiver station with active antennas in a CDMA mobile communication system, comprising a transceiver installed indoors for up-converting a CDMA-modulated signal to be transmitted to a service subscriber and down-converting a signal received from the subscriber into an intermediate frequency signal; a divider installed indoors for dividing a forward channel signal from the transceiver into a plurality of sector-unit forward channel signals; a coupler for coupling a plurality of sector-unit reverse channel signals and transferring the resultant signal to the transceiver; antenna interface means installed indoors for appending a DC voltage to each of the sector-unit forward channel signals from the divider, transferring the resultant sector-unit forward channel signals to a Butler matrix, receiving the sector-unit reverse channel signals from the Butler matrix and transferring them to the coupler; the Butler matrix being installed outdoors for making the sector-unit forward channel signals from the antenna interface means out of phase from one another to produce beam forming signals, converting a reverse channel signal into the sector-unit reverse channel signals and transferring them to the antenna interface means; and active radio frequency means installed outdoors for radiating each of the beam forming signals from the Butler matrix at a predetermined beam width and predetermined orientation angle over the air, receiving the reverse channel signal from the subscriber, amplifying it and transferring the resultant signal to the Butler matrix.
Preferably, the antenna interface means includes a power supply for converting an external commercial AC input voltage into a DC voltage to satisfy input conditions of the active radio frequency means; and first to third power/signal couplers for coupling the sector-unit forward channel signals from the divider with the DC voltage from the power supply, respectively.
Alternatively, the antenna interface means may include a power supply for converting an external commercial AC input voltage into a DC voltage desired by the active radio frequency means; a power control signal generator for communicating with indoor equipment to receive transmission/reception power control values therefrom and generating transmission/reception power control signals respectively according to the received power control values; transmission power control means for amplifying the sector-unit forward channel signals from the divider in response to the transmission power control signal from the power control signal generator, coupling each of the amplified sector-unit forward channel signals with the DC voltage from the power supply and transferring the resultant forward channel signals to the Butler matrix; and reception power control means for amplifying the sector-unit reverse channel signals from the Butler matrix in response to the reception power control signal from the power control signal generator and transferring the resultant reverse channel signals to the coupler.
Preferably, the transmission power control means includes first to third transmission power controllers, each of the transmission power controllers amplifying a corresponding one of the sector-unit forward channel signals from the divider in response to the transmission power control signal from the power control signal generator, coupling the amplified forward channel signal with the DC voltage from the power supply and transferring the resultant forward channel signal to the Butler matrix.
Each of the first to third transmission power controllers may include an amplifier for amplifying the corresponding sector-unit forward channel signal from the divider by a fixed gain; an attenuator for attenuating the amplified forward channel signal from the amplifier in response to the transmission power control signal from the power control signal generator; and a power/signal coupler for coupling the attenuated forward channel signal from the attenuator with the DC voltage from the power supply and transferring the resultant forward channel signal to the Butler matrix.
Preferably, the reception power control means includes first to third reception power controllers, each of the reception power controllers amplifying a corresponding one of the sector-unit reverse channel signals from the Butler matrix in response to the reception power control signal from the power control signal generator and transferring the amplified sector-unit reverse channel signal to the coupler.
Each of the first to third reception power controllers may include an amplifier for amplifying the corresponding sector-unit reverse channel signal from the Butler matrix by a fixed gain; and an attenuator for attenuating the amplified reverse channel signal from the amplifier in response to the reception power control signal from the power control signal generator and transferring the attenuated reverse channel signal to the coupler.